The present invention relates to a printhead, a printing apparatus using the same, and a printhead control method and, more particularly, to exchange of data between the printhead and the printing apparatus using the same.
Note that the present invention is applicable not only to a general printing apparatus but also to a copying machine, a facsimile apparatus having a communication system, a word processor having a printing unit, and an industrial printing apparatus combined with various processors.
An example of information output apparatuses in a word processor, personal computer, facsimile apparatus, and the like is a printer for printing information such as desired characters and images on a sheet-like printing medium such as a paper sheet or film.
As the printing method of the printer, various methods have been known. In recent years, an inkjet method receives a great deal of attention because information can be printed on a printing medium such as a paper sheet in a non-contact manner, and color information can be easily printed, and printing is very quiet. As the inkjet method, a serial printing method of mounting a printhead for discharging ink in accordance with desired printing information, and printing the information while reciprocally scanning the printhead in a direction perpendicular to the feeding direction of a printing medium such as a paper sheet is widely used because of low cost and small size.
Data such as printing information to be input to the printhead is generally input to the printhead in synchronism with an externally applied clock signal.
As disclosed in Japanese Patent Laid-Open No. 10-251479, the printhead incorporates a temperature sensor, an A/D converter for converting an output from the temperature sensor into digital information and outputting the digital information as a pulse signal, and a memory for storing element characteristics based on variations in printing elements during the manufacture process. In reading such information from the printhead, data is output from the printhead in synchronism with an externally supplied clock signal.
To simplify the internal circuit of the printhead, the same clock signal is used to input and read these data, and the same frequency is used to input and data to and from the printhead.
In recent years, as the printing density (number of printing pixels) increases, a higher printing speed is required. To achieve this, the printhead must be constituted by many printing elements (nozzles) at high density, and the frequency of driving each printing element and the printing data transfer speed must be increased.
If the frequency of a clock signal serving as the reference of the printing data transfer speed is increased, the response speed of an analog circuit for processing an output from a sensor arranged in the printhead must be increased in reading data from the printhead.
Especially when an output from the temperature sensor in the printhead is converted into a digital signal by an A/D converter arranged inside the printhead, and transmitted to the printer main body, the response speeds of the A/D converter and output circuit must be increased to output the digital signal in synchronism with a clock signal whose frequency is increased for a high printing speed. As a result, the yield decreases due to a small design margin, and the circuit scale increases.
In addition, a high-frequency clock signal readily generates high-frequency noise inside the printhead or at a wiring portion where the printhead is connected to the printer main body. This noise affects a circuit such as an A/D converter for processing an analog signal, and output data degrades.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a printhead capable of outputting information about the state of the printhead at a proper speed while increasing the printing data input speed, a printing apparatus using the same, and a printhead control method.
To achieve the above object, according to the present invention, a printhead which has a plurality of printing elements and drives each printing element in accordance with input printing data to perform printing comprises a clock signal input terminal for externally receiving a plurality of clock signals having different frequencies, input means for converting the printing data input in synchronism with a clock signal having a first frequency supplied to the clock signal input terminal into data corresponding to the printing elements, and output means for externally outputting information about a state of the printhead in synchronism with a clock signal which is supplied to the clock signal input terminal and has a second frequency lower than the first frequency.
The above object can also be achieved by a printing apparatus according to the present invention which performs printing using this printhead, and comprises clock signal generation means for generating clock signals having the first and second frequencies.
To achieve the above object, according to the present invention, a control method for a printhead which has a plurality of printing elements and drives each printing element in accordance with input printing data to perform printing comprises the input step of converting the printing data input in synchronism with an externally supplied clock signal having a first frequency into data corresponding to the printing elements, the output step of externally outputting information about a state of the printhead in synchronism with an externally supplied clock signal having a second frequency lower than the first frequency, and the control step of controlling operation states in the input and output steps in accordance with a frequency of an externally supplied clock signal.
In the present invention, the printing apparatus main body supplies clock signals having a first frequency and a second frequency lower than the first frequency. Printing data which influences an increase in printing speed is input in synchronism with the first clock signal, and information about the state of the printhead is output in synchronism with the second clock signal.
In reading from a sensor or memory arranged inside the printhead that does not influence the printing speed, a clock having a low frequency is used in consideration of the response speed of a circuit whose speed is difficult to increase, while increasing the printing speed. This suppresses an increase in circuit scale, an increase in the precision of a component used, and an increase in cost. Further, output information about the state of the printhead is prevented from being degraded by high-frequency noise generated by a clock.
Input and output operation states are preferably controlled in response to the frequency of a clock signal supplied to the clock signal input terminal.
Information about the state of the printhead preferably includes the characteristics of the printing element.
Information about the state of the printhead preferably includes an output from a sensor arranged inside the printhead, and the output from the sensor is preferably converted into a digital signal.
In this case, an example of the sensor is a temperature sensor for measuring the temperature of the printhead.
The clock signal supplied to the clock signal input terminal is preferably frequency-divided, and the output means preferably outputs a digital signal converted by A/D conversion means, in synchronism with a signal obtained by frequency-dividing the clock signal having the second frequency.